Well a good way could be thinking "is it worth it, can't I wait until the next meal to eat"? Im also 13 so I feel the struggle.
Hello I'm 12 and I'm trying to lose weight as well so here's my way for you to stop snacking.
1. Distract yourself with whatever you like to do
2. Drink lots of water(it's a good weight loss weapon)
3. Exercise just before a meal
4. Read quotes on google images about "Not giving up" or "weight loss quotes"